Explanation of Plate 2. 



Figure: 1. — Melonites multiporus, Norw. and Owen ; spines. Specimen in Museum of 

 Comparative Zoology, catalogue number 2988. Magnified 6 -[- di- 

 ameters. Page 137. 



Figure 2. — Melonites multiporus ; viewed from oral end. The 5 ambulacral areas 

 have 4 columns ventraUy ; 3 interambulacra, A, C and I, have 2 plates 

 ventrally; 2 areas, ^ and G, have 3 plates ventraUy. if = remnant 

 of perignathic girdle. Specimen in Museum of Comparative Zoology, 

 catalogue number 3000. Magnified 1^ diameters. Pages 140, 142. 



Figure 3. — Melonites multiporus ; ventral border of corona. The ambulacral areas 

 terminate in 4 plates, except area /, which is wanting ventrally. 

 The interambulacra terminate ventrally in 2 plates. Specimen in 

 Museum of Comparative Zoology, catalogue number 3003. Magnified 

 1^ diameters. Page 142. 



Figure 4. — Melonites multiporus; development of ambulacrum. The 4 columns at 

 the base, a, a^ and ¥, b, are extended dorsally as the 2 median and 

 2 outer columns of the area. New columns, c, d, e, f, are intro- 

 duced in the median portion of each half-area. Museum of Com- 

 parative Zoology, catalogue number 2994. Magnified 4 diameters. 

 Compare figure 1, page 191, and plate 4, figure 18. Page 140. 



Figure 5. — Melonites multiporus ; cross-section of ambulacrum ; I, I, adambulacral 

 plates; a, b, the 2 outer; a^, b\ the 2 median columns of ambu- 

 lacral plates. Pores pass from the outer border of the plate on the 

 distal side to the median or inner side of the plate on the proximal 

 side. The dotted portions of the pores are reconstructions, not being 

 shown in the section. Plate X does not show the pores in the plane 

 of this section. Specimen in Museum of Comparative Zoology, cata- 

 logue number 3030. Magnified 2 diameters. Pages 141, 154. 



Figure 6. — Melonites multiporus ; showing variation ; column 9 originates in a tetrag- 

 onal instead of a pentagonal plate ; 2 adjacent heptagons exist instead 

 of one. Specimen in Museum, of Comparative Zoology, catalogue 

 number 3017. (Area J, see tabulation, page 169). Magnified 3 

 diameters. Page 154. 



Figure 7. — Melonites multiporus ; interambulacrum, showing variation; the initial 

 plate of column 6 is tetragonal, the heptagon associated with pen- 

 tagon 8 occurs in the fifth instead of the seventh column, a rare 

 variation. The ninth column at its origin has five columns on the 

 left and three on the right, a very unusual variation (compare with 

 table, page 167)- Specimen in Museum of Comparative Zoology, 

 catalogue number 3021. Life size. Page 159. 

 All the specimens ou this plate are from the Subcarboniferous, Saint Louis group, 



Saint Louis, Missouri. 



247 



